The present invention relates generally to an apparatus for electrolytically refining nuclear fuel, and specifically to a nuclear fuel electrorefiner for recovering substantially purified uranium from nuclear fuels having a zirconium matrix and from nuclear fuels which do not have a zirconium matrix.
Spent nuclear fuel generally contains unused fissionable materials, including uranium. It is desirable to treat the spent nuclear fuel to remove the unused fissionable materials for ease if disposal as waste or for integration into newly manufactured nuclear fuels. Currently, spent metal fuel is electrolytically refined using an electrorefiner, which typically includes an anode in the form of a basket containing spent nuclear fuel, and a cathode for deposition of uranium, both submerged within a molten electrolyte pool. When a potential is placed across the anode and cathode, the nuclear fuel dissolves and uranium is electrolytically deposited on the cathode.
However, spent nuclear fuel also contains noble-metal and reactive fission products, actinides, and other metals such as zirconium which were present in the original fuel. When the spent nuclear fuel dissolves, if migration of the noble-metal fission products to the cathode is not prevented, then they will contaminate the uranium deposited on the cathode.
In general, where the nuclear fuel contains a zirconium matrix, the fate of the noble-metal fission products is tied to the dissolution of zirconium, such that the noble-metal fission products are retained with undissolved zirconium. Therefore, by limiting the dissolution of zirconium, the amount of noble-metal released into the electrolyte can be reduced, thus limiting the contamination of the uranium deposited at the cathode. Zirconium dissolution is controlled by limiting the current supplied to the fuel dissolution basket which, in turn, results in a longer amount of time necessary to dissolve the target uranium.
In addition, limiting the dissolution of zirconium also limits the dissolution of uranium, and therefore limits the amount of recoverable uranium. Further, where the spent fuel lacks a zirconium matrix (or other metal capable of retaining the noble-metal fission products), separation of the noble-metal fission products from the target unused fission materials (i.e. uranium) becomes impossible. Therefore, there is a present need for an apparatus and process capable of refining spent nuclear fuels which do not have a zirconium matrix.
Further, there is a need for an apparatus and process capable of refining spent nuclear fuels which contain a zirconium matrix, without the need for limiting the dissolution of zirconium while attempting to limit contamination at the cathode.
Therefore, it is a first object of the present invention to provide a process and apparatus capable of substantially separating noble-metal fission products from target unused fission materials, regardless of the matrix employed.
It is a second object of the present invention to provide a process and apparatus for refining nuclear fuel which provides both predictable and repeatable recovery of uranium.
It is a third object of the present invention to provide a process and apparatus having an enhanced throughput.
It is a further object of the present invention to provide a process and apparatus which requires fewer deposition steps.
Another object of the present invention is to provide an apparatus which can refine nuclear fuel in a shorter amount of time than conventional nuclear fuel electrorefiners.
The above-listed objects are met or exceeded by the present nuclear fuel electrorefiner for recovering substantially purified uranium from nuclear fuels having a zirconium matrix and from nuclear fuels which do not have a zirconium matrix. The electrorefiner includes a vessel having an anodic fuel dissolution basket and a high-efficiency cathode suspended therein. The high-efficiency cathode and fuel dissolution basket are suspended in a molten electrolyte pool, typically of mixed metal chlorides such as a eutectic salt of LiClxe2x80x94KCl, the electrolyte floating on a cadmium pool.
An electrical-power supply in selective electrical communication with the fuel dissolution basket and high-efficiency cathode provides electrical power to the electrorefiner.
A shroud surrounds the fuel dissolution basket, and the shroud is positioned so as to separate the electrolyte pool into an isolated electrolyte pool within the shroud and a bulk electrolyte pool outside the shroud.
In operation, spent nuclear fuel is chopped into small segments which are placed within the fuel dissolution basket. Application of a potential across the fuel dissolution basket and high-efficiency cathode causes the nuclear fuel to dissolve. Unwanted noble-metal fission products and matrix material transfer to the electrolyte within the shroud and to the cadmium pool forming precipitates which are removed by a filter and separator assembly. Uranium values are transported by the cadmium pool from the isolated electrolyte pool to the bulk electrolyte pool, and then to the high-efficiency cathode where they are electrolytically deposited. The high-efficiency cathode includes a mandrel for collecting electrolytically deposited material and a collection basket below the mandrel substantially preventing electrolytically deposited material separated from the mandrel from dropping into the cadmium pool.